1. Field of the Invention
The invention relates to thermoplastic fasteners for joining articles, and particularly to fiber reinforced thermoplastic composite fasteners.
2. Description of the Prior Art
The prior art includes a number of plastic fasteners which are utilized in combination with heat to join articles. Some of these fasteners include fiber reinforcing materials.
For example, U.S. Pat. No. 4,478,544 to Strand discloses a composite rivet having a thermoset matrix with carbon fiber reinforcing. The rivet is placed through preformed holes in two sheets which are to be joined, and then an enlarged head is formed on the rivet by the application of heat and pressure.
It is also known that plastic fasteners can be deformed through the use of ultrasonic heating devices, as shown in U.S. Pat. No. 3,499,808 to Obeda.
The art includes sharpened plastic fasteners such as staples, as seen in U.S. Pat. No. 4,281,785 to Brooks. The plastic staples of Brooks are not reinforced. The staples are driven through layers of fabric and then heated to join the two legs of the staple and hold the same in place.
U.S. Pat. No. 4,478,661 to Lewis discloses the use of thermoplastic thread or thermoplastic staples to join thermoplastic sheets.
U.S. Pat. No. 4,582,236 to Hirose discloses the use of synthetic resin tacks or staples which are driven through preformed holes in adjacent sheets of material and then heated to form rivet heads.
In all of the examples discussed above, the fastener is either placed through a preformed aperture, or a sharpened fastener is driven through a relatively pliable material without the prior application of any heat. The methods described in the cited references are not suitable for joining articles where one of the articles is a thermoplastic article which does not have a preformed aperture for receiving the fastener and which is of sufficient thickness and strength that a fastener cannot be readily driven therethrough. The present invention, however, provides methods and fasteners directed to just such a situation.